Variable cam timing (VCT) systems are used in internal combustion engines to advance or retard valve timing, to thereby adjust combustion operation over a range of engine operating conditions. Adjusting valve timing in this way increases combustion efficiency and engine power output, and reduces emissions.
To fix the range of valve advancement or retardation, fully advanced and fully retarded locking devices are used in some VCT systems. Mid-locking devices may also be in VCT systems to substantially fix the cam phasing in a position between fully advanced and fully retarded (e.g., a neutral position) during certain operating conditions. U.S. Pat. No. 6,330,870 discloses an engine with an intake and exhaust lock mechanism for locking the intake and exhaust valve timing adjusters in intermediate positions between fully retarded and fully advanced positions. Separate hydraulic control valves are used to control the intake lock mechanism and the exhaust lock mechanism.
However, the Inventors have recognized several drawbacks with the VCT system disclosed in U.S. Pat. No. 6,330,870 as well as other mid-locking VCT systems. For example, a large number of hydraulic valves are used for providing the mid-locking functionality. For example, U.S. Pat. No. 6,330,870 provides a separate hydraulic control valve for each mid-locking mechanism. In other systems, two separate valves may be used to control each mid-locking device (e.g., an intake-side mid-locking device and an exhaust-side mid-locking device). Moreover, in some VCT systems, separate hydraulic valves may be used to adjust the phasing of the valve timing actuators. As result, the cost and complexity of the VCT system is increased. Moreover, when the number of parts in the VCT system is increased, the likelihood of component malfunction and repair/warranty costs is increased. These problems may be exacerbated in engines having two cylinder banks, such as V-type engines, resulting in another doubling of the number of hydraulic valves in the VCT system.
The Inventors herein have recognized the above issues and identified a method for operation of an engine is provided. The method includes operating an engine with independent variable intake and exhaust valve timing with an intake valve timing actuator and an exhaust valve timing actuator, locking both the intake and exhaust valve timing actuators in a mid-lock position, and unlocking both the intake and exhaust valve timing actuators via a common locking-control valve. For example, by hydraulically linking the locking/unlocking devices of both the intake and exhaust phasers with a mid-lock position on a cylinder bank to a common control valve, electronic control of the common valve can control locking/unlocking of both the intake and exhaust camshafts concurrently. Further, it is possible to do so while still maintaining desired performance for both the intake and exhaust phasers during various operating conditions, including cold starting.
In this way, the number of control valves in the VCT system may be reduced when compared to VCT systems which may include one or more control valves per locking mechanism. As a result, the cost and complexity of the engine may be reduced. Moreover, repair costs for the VCT system may be reduced and the likelihood of VCT malfunction may also be reduced.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Additionally, the above issues have been recognized by the inventors herein, and are not admitted to be known.